The present invention relates to an artificial tooth and a process for making an artificial tooth.
It is known to use polymerizable material in the dental practice which is hardenable into its finished condition by light or thermal polymerization thereof as well as, in some instances, by the application of pressure thereto. In order to undertake a light hardening process, the light must have an undisturbed access to the mass to be polymerized, whereby it has become conventional to provide transparent molds for the prostheses themselves. A solution of this type is disclosed in DE-OS 36 10 683. In this disclosed tooth prosthesis, an especially polymerizable mass is used for the production of a form or mold piece which remains white in color and which is comprised of, among other components, urethane oligomers. A model for the prosthesis is produced in connection with the manufacture of such a prosthesis with the model having a transparent mold overpiece. A disadvantage of this approach is, however, the substantial effort required for the separate production of a soft elastic mold component which is to be combined with a completely hardened artificial or plastic material.
It has further already been suggested to produce an artificial tooth comprised entirely of light polymerizable material. Such artificial teeth must be especially wear-resistant, so that the surface quality of the teeth is measured against stringent standards. This process has not yet found any acceptance in practice.
Artificial teeth are much more typically comprised of a ceramic mass. A tooth produced in this manner is relatively hard and exhibits a good surface quality. The tooth is also wear-resistant and is sufficient, when produced with corresponding care and the use of corresponding forming techniques, to satisfy today's aesthetic demands. A certain disadvantage of teeth produced of ceramic sinter masses is that these teeth have a surface which is harder than the natural tooth bloom.
Thus, those surfaces of teeth in the mouth of the patient which are in opposition to the artificial tooth are placed under relatively strong demands. On the other hand, artificial or composite material teeth have the advantage that they are, at least, somewhat softer than natural teeth. Artificial teeth, i.e. teeth of polymeric material, have, in contrast to ceramic teeth, certain advantages, whereby a reduced wearing away of the oppositional surfaces relative to the inserted artificial teeth is one of these advantages.
Plastic or artificial material is, on the other hand, less resistant to pressure and is correspondingly more susceptible to wear than ceramic so that, in the production of such artificial teeth, care must be paid to ensure that the potentially achievable material properties are optimized.
In order to produce an artificial tooth which is particularly resistant to wear and that is hard, selected plastic or artificial material is used such as, typically, a methyl methacrylate derivative. Evaluations have shown that the manner of the polymerization, and the care exercised in performing such polymerization, is a decisive factor in determining the surface quality and the surface hardness of the artificial tooth produced by this process. In this connection, an artificial tooth is typically polymerized under comparatively high pressure at a correspondingly increased or raised temperature.
In order to meet the aesthetic demands of the present day dental practice, differing or varying layers are used—namely, a transparent layer, which is intended to simulate the natural tooth bloom, and an opaque layer, which is intended to simulate the tooth bone. These layers are each produced under a corresponding pressure and corresponding temperature in connection with their polymerization and each forms a respective shell-shaped body. In connection with this approach, care must be taken that a secure connection between the layers is ensured so that the artificial tooth does not come apart into its individual components.
This process is, however, one which requires substantial effort in that a multitude of molds and/or mold inserts must be used which must be regularly cooled in an alternating manner and must also be regularly heated or warmed in an alternating manner. A further problem lies in the fact that the artificial material is subjected to a multiple—for example, four-fold—heating up beyond its melting point and is then subjected to an intensive cooling off, all of which leads to a deterioration or negative impact on its material properties. On the other hand, it is practically not possible to heat and put under pressure only that sole layer which is to be completely hardened for the reason that the layer lies in close relationship to the neighboring layer unless completely separate forms or molds are used. In spite of these disadvantages, there have been heretofore no alternative approaches for optimizing the production of artificial teeth.